Bullae (containing purulent fluid)

The diameter of the blister is generally less than 1cm, and those who exceed 1cm are called bullae. Some scholars also use 0.5cm as the boundary to distinguish blisters from bullae. Blisters and bullae can be distributed one by one, such as pemphigoid; they can also be clustered, such as shingles. The blister contains serous fluid, which is pale yellow; the blister contains blood, which is red (called a blood blister); the blister contains lymph fluid, which is clear and transparent; the pus contains pus, which is cloudy. Serous blister can turn into a pustule or blood blister. The shape of the blister is various, it can be semi-circular, conical, oblate or irregular, and some have umbilical fossa in the center. The blister wall can be tense and bright like a balloon; it can also be loose, like wrinkled paper. Pustules can occur on normal skin, or on skin with inflammation. There can be redness around the pimples, or nothing. The blister is contained in the skin, and can be divided into subcorneal blisters due to the different depth of the site, such as white pupa (also in the cornea); epidermal blisters and bullae, such as herpes simplex, chicken pox, pemphigoid, etc ; Epidermal bullous, such as bullous pemphigoid, erythema polymorpha. The blister can be single or multi-chamber.